Examples of such a conventional apparatus includes a printer, a reader, a show-through image data generating unit, a corrected back inspecting image data generating unit, and a determining unit. The printer performs printing to a front face of a printing sheet in response to data on an original front image, and performs printing on a back face of the printing sheet in response to data on an original back image. The reader reads out the front and back images of the printing sheet from the printer to obtain front inspecting image data and back inspecting image data, respectively. The show-through image data generating unit corrects shading of the front inspecting image data obtained by the reader in accordance with transmittance of the printing sheet after performing the printing on the front face and before performing the printing on the back face, and inverting the front image to generate show-through image data. The corrected back inspecting image data generating unit subtracts the show-through image data from the back inspecting image data obtained by the reader to generate corrected back inspecting image data. The determining unit collates the original back image data with the corrected back inspecting image data to determine quality of the printing on the back face. See, for example, Japanese Patent Publication No. 4265421A.